Comments from procps code:
The Open Group Base Specifications Issue 6 (IEEE Std 1003.1, 2004
Edition) requires that user and group names print as decimal numbers
if there is not enough room in the column, so tough luck if you don't
like it.
The UNIX and POSIX way to change column width is to rename it:
ps -o pid,user=CumbersomeUserNames -o comm
The easy way is to directly specify the desired width:
ps -o pid,user:19,comm

Note

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